Vesicles or liposomes made of lipid are mostly constituted of an amphipathic substance, phospholipid (Patent Literature 1, Patent Literature 2, Patent Literature 3, and Patent Literature 4). Phospholipid is a major structural component of natural membrane and a lipid vesicle is suitable as a model for studying the natural membrane.
However, phospholipid per se is unstable and decomposes in the absence of an antioxidant. Also high cost in synthesis and purification is a problem. A vesicle per se made of an unstable substance is also unstable. This is also a problem.
In the case of a cationic or an anionic vesicle composition, the vesicle breaks down if pH changes, and becomes no longer stable. If the vesicle is charged with active ingredients, these are released from the vesicle. For example, even if a high-crystalline component like a ceramide, which effectively works for skin roughness, is stabilized in a vesicle, if the vesicle is broken down by the effect of pH, a ceramide is crystallized and loses the effect. Furthermore, an active ingredient stable in a vesicle, if it is released from the vesicle by breakage due to the effect of pH, is decomposed and the effect cannot be obtained. These problems occur.